1. Field of the Invention
This invention relates to a method for increasing mobility of polymer blends.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers in bracketed superscripts [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Conjugated polymer-based organic field-effect transistors (OFETs) are of interest since the solution processability of the semiconductor material raises the possibility of lower device fabrication costs.[1] Markedly improved device performances (since their initial development) suggests commercial viability.[2-5] Substantial progress has been achieved on the design of high mobility polymers and small molecules by tuning molecular structure.[6,7] Processing conditions and device architecture have also been modified to achieve high mobility.[1,8-13] Further improvements in OFET processing, for example by using non-specialized deposition techniques and by minimizing the volume of semiconductor included in the fabrication process while keeping relevant OFET performance, are also important considerations when considering practical implementation and widespread impact.[14,15]
One strategy for improving operational properties and lowering the cost of organic electronic devices has been to combine the optoelectronic properties of the organic semiconductor with a commodity insulating polymer.[15-26] In addition to reducing materials costs, these commonly-available polymers have the potential to enhance environmental stability and improve mechanical properties when blended with the semiconductor component.[15,16] Multicomponent OFETs have been studied, and these efforts lay the foundation for understanding blend strategies, the impact of dilution on charge carrier transport, and the specific challenges for implementation. An early study demonstrated that the hole mobility for pristine poly(3-hexylthiophene) (P3HT) was in a range from 0.008-0.02 cm2V−1 s−1, while devices fabricated from a solution of 90% P3HT/10% polystyrene (PS) had a mobility decreased to 5.5×10−3 cm2V−1 s−1.[17] More recently, insulator composition-independent mobility has been achieved in other systems through a variety of processing modifications. For example, by blending 5 wt % poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) with PS and in the presence of TCNQ, mobilities of 0.4 cm2V−1 s−1 were obtained, which are among the highest for all-polymer, majority-insulator OFETs.[20]